Crops such as corn and soybeans are grown in North America primarily to provide a source of animal feed. The flesh and other products from the animals eventually provide a major source of nutritional human food. Accordingly, not only is it desirable to promote the rate of growth of plants and the quantity of edible feed which such plants will yield, but also it is desirable to ensure that such plants contain quantities of trace elements required for good human diet.
It is known that a variety of trace elements should be present in human foodstuffs, to provide a healthy, balanced diet. For example, a certain minimum level of chromium is desirable. For animal metabolism, chromium has to be incorporated in a tetra-aquo-dinicotinato compound, called glucose-tolerance-factor (GTF). Chromium GTF is metabolized in a different way from inorganic chromium.
Chromium plays a role of considerable significance in glucose metabolism and in cardiovascular disease. A number of therapeutic trials of human dietary chromium supplementation have indicated that chromium deficiency can be a cause or an aggravating factor in the glucose intolerance of infants suffering from protein calorie malnutrition, of maturity-onset diabetics, and of middle-aged and elderly subjects. It has been found that the diets of North American residents tend to be deficient in chromium, to some extent because a significant constituent of their diet is the meat of animals which have been corn fed, many of the high yielding corns traditionally being short of chromium.
Zinc is another trace element which is essential in human diets, in a least a certain minimum level. Zinc deficient diets lead to anorexia, lack of growth, and teratogenesis. Zinc is involved in protein synthesis. Its deficiency in human diets is relatively common.
The presence of zinc in the soil of the growing environment is known to affect the growth of corn. Literature has taught that if the soil has a zinc deficiency, then corn plants grown therein tend to be stunted, and exhibit leaf, stem and root abnormalities. Zinc deficiency in germinating seeds is especially acute as the seed must carry its entire complement of zinc if it is to experience growth at temperatures below 17.degree. C. Zinc deficiency may lead to the death of the plant before the soil warms up. The application of certain phosphorus-rich fertilizers is known to cause zinc deficiency in plants. Loneragan et al. (1982), who studied this zinc-phosphorus relationship, observed that under conditions of high phosphorus supply and low zinc supply phosphorus is absorbed by the roots and transported in such excess that it becomes toxic and produces symptoms resembling zinc deficiency, while not changing the zinc concentration in the plant tops. Singh et al. (Agronomy Journal, Vol. 78, July-August, 1986) have suggested that increased phosphorus levels may lead to this reduced zinc uptake via a biological route, namely the reduction of vesicular-arbuscular-mycorrhizal (VAM) infection of the plant. Consequently, many commercially available fertilizers contain added zinc so as to ensure that the soil of the growing environment is sufficiently rich in zinc prior to planting. The presence of adequate total concentrations of zinc in the soil of the growing environment does not; however, necessarily mean that a growing plant will take up the zinc to the most beneficial extent. Marginal zinc deficiency often goes undetected, but can have a drastic effect on plant growth.
Mycorrhizal fungi are a special type of fungus commonly present in the soil which penetrate the root cortex of their specific host plant and subsequently enter into a symbiotic relationship with the plant. In this relationship most but not all nutrients essential to the fungus are exuded from the plant membranes to the fungus, e.g., glucose and amino acids, and conversely, minerals such as phosphorus, potassium, zinc, calcium, copper, iron, magnesium, and manganese, are gathered up and delivered to the plant by the mycorrhiza in a more effective and economic manner than the plant could have gathered alone.
Hairs called hyphae grow out of the mycorrhiza and associate with the plant root in arbuscules or tree-like structures at which the nutrient exchange occurs. The hyphae also extend into the soil t o gather up trace minerals.
There are many varieties of mycorrhiza indigenous to soil, and each is specific for a particular host. Researchers have attempted to inoculate soil with a given beneficial mycorrhizal fungus corresponding to a particular plant. These attempts have met with little success, as these inoculated varieties lose out in biological competition to the less effective indigenous mycorrhiza. Accordingly, no enhancement of growth is demonstrated unless the soil is presterilized. A further problem is that mycorrhizal fungi suitable for enhancing growth of crops are not, as far as is known, lab-culturable. This makes their isolation extremely tedious and costly.
It would be beneficial to the plant that the number of host-specific mycorrhiza be increased in the vicinity of the seeds and later the roots, as these fungi increase the uptake of trace minerals to the plant.
It is known that germinating seeds, in addition to producing amino acids and glucose, produce and exude two volatile compounds, acetaldehyde, a growth retardant, and ethanol, a growth enhancer. Norton and Harmon (Canadian J. Bot, Vol. 63, 1985) found that exposure to the volatiles from aged pea seeds stimulated soil microbial activity. Hyphae grew out from the mycorrhizal organisms preferentially towards the ethanol exuded from the aged pea seeds. Ethanol enhances the growth of free-living rhizobia.
It is an object of this invention to provide novel beneficial seed dressing compositions for application to crop seeds, to enhance symbiotic microbial benefit with a sugar environment around the seed and GTF chromium as a nutrient to promote fungi growth and ethanol production.
It is a further object to provide a novel process for growing agricultural crops.